It is known in the medical field to use afterloader devices in the treatment of cancerous tumours using radioactive sources having intensity greater than that which can safely be handled. Remote afterloaders are devices generally used in the cancer treatment field to accurately advance and retract a flexible wire containing an electro-magnetic radiation emitting source over a specified distance for a specific time period. A remote afterloader comprises a flexible simulation wire for testing purposes and a flexible wire with the electro-magnetic radiation emitting source, controllers and transport mechanisms to operate both types of wires, as well as a radiation shielded housing for the radiation emitting source.
Typically one or more catheters, needles, or other closed pathways (hereafter “guide tubes”) to the treatment site are positioned in the patient. The guide tubes are then attached to the afterloader, which advances the radioactive source at the end of the transport wire, sometimes called a source-wire, along the guide tubes according to a predetermined sequence calculated to deliver a therapeutic dose of radiation to the tumour. Many of these prior art devices advance the source-wire by means of a friction drive belt trained about a wheel with the wire sandwiched between the belt and wheel.
The radiation emitting sources presently used are radioactive sources, e.g. in the form of implant seeds or in the form of radioactive sources which are inserted through a hollow guide tube towards the site of intended therapy by means of a transport wire, which sources continuously emit electro-magnetic radiation following the principles of natural radioactive decay and which are characterized by the specific half life time of the used radioactive material. Since the sources used in such treatment can constitute a hazard to a technician administering the treatment, afterloaders are used for inserting of the radioactive source and the treatment therewith in the patient with minimum radiation exposure of the technician or with no exposure whatsoever.
For minimising the exposure of radioactive radiation to the environment these afterloader devices require a heavily constructed and expensive radiation shielded housing. The known afterloader devices allow the insertion of the radioactive source in the patient after the technician administering the treatment moves away from the patient or leaves the treatment room. In other words, the radioactive source is loaded into the patient for treatment after the technician leaves the patient, and for that reason such devices are generally referred to as “afterloading devices”.
The effective treatment with a discreet radioactive source is dependent upon the particular tumour, the position of the tumour in the body, the activity of the source and the accuracy of positioning the source near or in the tumour. Such treatments involve an intrusion into the animal body, e.g. human body, and that intrusion may be through a natural orifice in the body, such as a blood vessel or lung trachea, if the tumour so admits, or by way of implanting flexible or rigid needles and other special devices in or near the tumour.
In either case, the effectiveness of the radiation treatment depends on accurately placing the radiation emitting source at the correct position near the tumour. With some tumours, a single radioactive source may be sufficient for effective treatment, but with other tumours, multiple sources, positioned in and around the tumour, may be required. In addition, with such multiple positioning of radioactive sources, the amount of radiation for effective treatment may vary with the different positioned sources, and therefore, specific regimens of treatment are often necessary in terms of both the positioning of the radiation emitting source and the duration of radiation exposure of the tumour.
Generally speaking, the radioactive sources used with these afterloading devices fall into two categories. The first category is that of a low dose rate (LDR) source, and the second category is that of a high dose rate (HDR) source. An LDR source emits low levels of radiation and can be safely handled by a technician for short periods of time. An HDR source emits high doses of radiation and cannot be safely handled by a technician, even for relative short periods of time. The after-loading devices for handling these two different radioactive sources are thus divided into two categories of machines, i.e. a low dose rate (LDR) machine and a high dose rate (HDR) machine.
An example of an afterloading device as described in the introduction is for example disclosed in U.S. Pat. No. 5,030,194. In that device a flexible wire is driven by suitable transport means together with a LDR or HDR source attached to one end from an outlet channel present a radiation shielded block or housing, through a guide tube and to the site of intended therapy in the patient by means of an applicator, e.g. an implant needle or catheter. Said applicator is positioned by a physician into the patient's body prior to the insertion of the radioactive source. The positioning of the needle or catheter into the body is sometime performed surgically and the correct position of that applicator near the site of the intended therapy is determined using suitable imaging techniques, like X-ray or ultrasound imaging means.
Effective treatment with a LDR source may often span many hours, e.g. 20 or 30 or even 50 hours. During such extended treatment, the patient can carry out normal body functions and the LDR source will likewise move in relation to the tumour. It is assumed that such movements will average out the radiation around the tumour and, therefore, a very accurate positioning of the LDR source, opposite the tumour, is not necessary.
However, the above assumptions are not always correct and incorrect positioned LDR sources may result. This results in less effective or ineffective therapy and, in addition, may unnecessarily expose healthy tissue to radiation. Thus, this procedure is less than desirable. In addition, it is often necessary to employ multiple LDR sources at different sites around the general site of intended therapy, even when treating a single localized tumour, since a single LDR source does not emit sufficient radiation to effectively treat many, even localized, tumours. In such case, the same procedure described above is used for each different site of intended therapy and the above-noted inaccuracies will affect the effectiveness of the radiation therapy.
With high dose rate (HDR) devices, the HDR source is too radioactive for operation in the manner of the LDR device. However the desired accuracy of the present HDR devices are even more hard to achieve, since exposure of the tumour to the high dose radiation is often only in terms of minutes, e.g. 10, 15 or 20 minutes, and a small inaccuracy in positioning the HDR source can result in large inaccuracies in effective treatment, in view of the short times involved.
Besides the negative effects relating to an inaccurate positioning of the radioactive source in the body and the undesired exposure to radioactive radiation of the technician the natural radioactive decay of the radioactive sources now used require a proper analysis of the decay state of the radioactive source before insertion into the body near the site of the intended therapy. This in order to obtain a correct calculation of the time, intensity and amount of the radiation emitted. However due to the natural radioactive decay of the radioactive source during time the actual radiation intensity and amount emitted during the treatment inside the patient body can differ (read: can be less) from the necessary radiation exposure (time and intensity) as planned prior to the treatment using suitable dosimetric therapy planning software.